1. Field of the Invention
The present invention relates to a rotary joint used to supply pressurized fluid, such as air and hydraulic oil, to a rotatable table of a rotary table assembly.
2. Description of the Related Art
A rotary joint of a rotary table assembly includes a rotational part attached to a rotatable table, a non-rotational part attached to a frame and a plurality of fluid passages formed in the rotational part and non-rotational part, and is used to supply pressurized fluid from the non-rotational part to the rotational part through the fluid passages. An example of conventional rotary joints is disclosed in Japanese Patent No. 3664471. The rotary joint in the patent disclosure is provided to a rotary table assembly including a rotatable table and a frame that rotatably supports the rotatable table from the back surface side of the rotatable table. To assemble the rotary table assembly, a hollow cylindrical shaft (rotational part) to be attached to the rotatable table and a columnar distributor (non-rotational part) to be attached to the frame are inserted together into the rotary table assembly from the back surface side of the rotatable table.
More details of the rotary joint disclosed in Japanese Patent No. 3664471 will be given. The columnar distributor is inserted into a center bore of the hollow cylindrical shaft. Around the outer peripheral surface of the hollow cylindrical shaft, an O ring is provided to prevent entry of foreign matter from the rotatable table side into the rotary table assembly. The O ring is disposed relatively near the rotatable table and interposed between the outer peripheral surface of the shaft and the inner peripheral surface of a support member on the rotatable table side.
The aforementioned conventional rotary joint has the following problems. The first problem is the long insertion distance. To insert a shaft into a rotary table assembly from the back surface side of a rotatable table, an end of the shaft, the end to be positioned on the rotatable table side, is first inserted and then the shaft is pushed in until passing through the rotary table assembly from one end to the other in an axial direction. The distance in which the shaft moves to be completely inserted in the rotary table assembly becomes long. During insertion, the O ring attached around the outer peripheral surface of the shaft makes sliding contact with the inner peripheral surface of the support member of the rotatable table, and consequently is torsionally deformed in the axial direction. The torsionally deformed O ring may remain in an improper shape at an improper position, and therefore may not be able to prevent entry of foreign matter.
The second problem is the inconvenience of attaching and replacing a large number of seals that are equidistantly disposed on the inner peripheral surface of the shaft in the axial direction and used to seal pressurized-fluid passages. In other words, because the shaft and distributor are axially long and thin, an operator cannot put his/her hand into the center bore of the shaft, and especially, cannot reach the rotational seals positioned away from opposite openings of the center bore.